Egg of the red-eared slider (Trachemys
scripta). Note the vascularized portion surrounding the embryo. The
temperature experienced during the middle third of incubation initiates
the cellular and molecular cascades that result in male or female offspring.
Incubation temperature is believed to activate genes encoding for the
steroidogenic enzymes aromatase and reductase, steroidogenic factor
1, and steroid hormone receptors.

The leopard gecko (Eublepharis macularius).
Incubation temperature influences body coloration, with individuals
from warmer temperatures having a lighter coloration. In this picture
the male (from a 32.5° C incubation temperature) is on the left
and the female (from a 26° C incubation temperature) is on the right.
In addition to determining the gonadal sex of the hatchling, incubation
temperature also influences growth rate and, in adulthood, the pattern
of secretion of sex hormone secretion, aggressive and sexual behavior,
and the size and metabolic activity of brain nuclei.

Pseudosexual behavior in the all-female
desert grasslands whiptail (Cnemidophorus uniparens). This is the characteristic
mating posture observed in all sexual whiptail lizards. Although males
do not exist in this parthenogenetic species, the individuals continue
to display male-like and female-like pseudosexual behavior. The male-like
individual is postovulatory and the female-like individual is preovulatory.

The green anole lizard (Anolis carolinensis).
The picture shows a territorial males in a full aggressive display.
Not the saggital display and erection of the crest on the neck and back.
The colored throat fan, or dewlap, is extended, indicating that the
male is challenging another male.

During most of the warm summer months,
the Canadian red-sided garter snake (Thamnophis sirtalis parietalis)
leads a solitary existence. At two times of the year, spring and summer,
however, the animals mass together as they emerge from, or later return
to, underground overwintering hibernacula. Only during the spring is
the intense mating activity observed. All males emerge together and
await the solitary emergence of females over the next two-to-four weeks.
The picture shows a female as she emerges from the underground hibernaculum.
The males are attracted to a specific pheromone produced normally by
females. This results in "mating ball" forming. Usually on
a single female will be at the center of this writhing mass of snakes.
There are some male, however, who produce the female pheromone and confuse
other males in the mating ball. These "she-males" are more
likely to mate with a female in the mating ball.